A number of short (ca. 50 amino acid residues or fewer) linear or cyclic cytotoxic peptides have been isolated recently from a variety of sources. These include mellitin, from bee venom, the magainins, from frog skin, and cecropins, from insects (Maloy, et al., Biopolymers (Peptide Science) 37: 105-122 (1995)). Although of widely varying peptide sequences and structures, these peptides all contain multiple lysine and arginine residues, and, at physiological pH, carry a net positive charge. They also form amphipathic structures wherein one portion of the structure is hydrophilic while the other portion is hydrophobic.
The peptides appear to act solely by direct lysis of the cell membrane (Maloy et al., supra (1995)). In the current model, cell lysis is initiated by the electrostatic attraction of the positive charge on the peptide to the negative phosphate head groups at the exterior surface of the membrane phospholipid bilayer. This interaction leads to insertion of the hydrophobic portion of the protein into the membrane, thereby disrupting the membrane structure. The lytic peptides are, in general, more active against prokaryotic cells, such as bacteria and fungi, than eukaryotic cells. This has led to interest in these peptides as potential agents for the treatment of infections in humans (Maloy et al., supra (1995); Arrowood et al., J. Protozool. 38: 161S-163S (1991); Haynie et al., Antimicrob. Agents Chemotherapy 39: 301-307 (1995).
The natural cytotoxic peptides, however, suffer from several disadvantages with respect to their use as human therapeutic agents. First, it appears that these peptides have evolved to act at high concentration at specific localized sites. Thus, when administered as a drug, the dosage necessary to attain an effective concentration at site of infection can be prohibitively high. A second disadvantage is the difficulty of isolating useful amounts of these peptides from the natural sources, along with the high cost of synthesizing useful amounts of peptides in this size regime. Finally, these compounds, like other peptides, are degraded in the gastrointestinal tract, and, thus, cannot be administered orally.
There is a need for anti-microbial agents which possess the broad activity spectrum of the natural cytotoxic peptides, but are inexpensive to produce, can be administered orally and have lower concentration requirements for therapeutic activity.
One aspect of the present invention is a method for treating a microbial infection in a mammal, comprising administering to the mammal a therapeutically effective amount of a polymer having an amine or ammonium group connected to the polymer backbone by an aliphatic spacer group.
The polymer to be administered can be a homopolymer or a copolymer. In one embodiment, the polymer further includes a monomer comprising a hydrophobic group, such as an aryl group or a normal or branched C3-C18-alkyl group.
The polymer to be administered can, optionally, further include a monomer comprising a neutral hydrophilic group, such as a hydroxyl group or an amide group.
Another aspect of the invention is a method for treating a microbial infection in a mammal, such as a human, comprising administering to the mammal a therapeutically effective amount of a polymer comprising a polymethylene backbone which is interrupted at one or more points by a quaternary ammonium group.
The present method has several advantages. For example, the polymers employed are easily prepared using standard techniques of polymer synthesis and inexpensive starting materials. The polymers will not be substantially degraded in the digestive tract and, therefore, can be administered orally. Polymer compositions can also be readily varied, to optimize properties such as solubility or water swellability and antimicrobial activity. Finally, the polymers to be administered include amine or ammonium functional groups attached to the polymer backbone via aliphatic spacer groups. The structural flexibility of such spacer groups minimizes backbone constraints on the interaction of the ammonium groups with anionic targets.
The present invention relates to a method for preventing or treating a microbial infection in a mammal, such as a human, by administering to the mammal a therapeutically effective amount of a polymer comprising a plurality of amino or ammonium groups which are attached to the polymer backbone via aliphatic spacer groups.
As used herein, a xe2x80x9ctherapeutically effective amountxe2x80x9d is an amount sufficient to inhibit, partially or totally, a microbial infection or to reverse development of a microbial infection or prevent or reduce its further progression. The term xe2x80x9cpolymerxe2x80x9d refers to a macromolecule comprising a plurality of repeat units or monomers. The term includes homopolymers, which are formed from a singly type of monomer, and copolymers, which are formed of two or more different monomers. A xe2x80x9cterpolymerxe2x80x9d is a copolymer formed from three different monomers. The term polymer, as used herein, is intended to exclude proteins, peptides, polypeptides and proteinaceous materials.
As used herein, the term xe2x80x9cpolymer backbonexe2x80x9d or xe2x80x9cbackbonexe2x80x9d refers to that portion of the polymer which is a continuous chain, comprising the bonds which are formed between monomers upon polymerization. The composition of the polymer backbone can be described in terms of the identity of the monomers from which it is formed, without regard to the composition of branches, or side chains, off of the polymer backbone. Thus, a poly(acrylamide) polymer is said to have a poly(acrylamide) backbone, without regard to the substituents on the acrylamide nitrogen atom, which are components of the polymer side chains. A poly(acrylamide-co-styrene) copolymer, for example, is said to have a mixed acrylamide/styrene backbone.
The term xe2x80x9cpolymer side chainxe2x80x9d or xe2x80x9cside chainxe2x80x9d refers to the portion of a monomer which, following polymerization, forms a branch off of the polymer backbone. In a homopolymer all of the polymer side chains are identical. A copolymer can comprise two or more distinct side chains. When a side chain comprises an ionic unit, for example, the ionic unit depends from, or is a substituent of, the polymer backbone, and is referred to as a xe2x80x9cpendant ionic unitxe2x80x9d. The term xe2x80x9cspacer groupxe2x80x9d, as used herein, refers to a polyvalent molecular fragment which is a component of a polymer side chain and connects a pendant moiety to the polymer backbone. The term xe2x80x9caliphatic spacer groupxe2x80x9d refers to a spacer group which does not include an aromatic unit, such as a phenylene unit.
The term xe2x80x9caddition polymerxe2x80x9d, as used herein, is a polymer formed by the addition of monomers without the consequent release of a small molecule. A common type of addition polymer is formed by polymerizing olefinic monomers, wherein monomers are joined by the formation of a carbonxe2x80x94carbon bonds between monomers, without the loss of any atoms which compose the unreacted monomers.
The term xe2x80x9cmonomerxe2x80x9d, as used herein, refers to both (a) a single molecule comprising one or more polymerizable functional groups prior to or following polymerization, and (b) a repeat unit of a polymer. An unpolymerized monomer capable of addition polymerization, can, for example, comprise an olefinic bond which is lost upon polymerization.
The quantity of a given polymer to be administered will be determined on an individual basis and will be determined, at least in part, by consideration of the individual""s size, the severity of symptoms to be treated and the result sought. The polymer can be administered alone or in a pharmaceutical composition comprising the polymer, an acceptable carrier or diluent and, optionally, one or more additional drugs.
The polymers can be administered, for example, topically, orally, intranasally, or rectally. The form in which the agent is administered, for example, powder, tablet, capsule, solution, or emulsion, depends in part on the route by which it is administered. The therapeutically effective amount can be administered in a series of doses separated by appropriate time intervals, such as hours.
Microbial infections which can be treated or prevented by the method of the present invention include bacterial infections, such as infection by Streptococcus, including Streptococcus mutans, Streptococcus salivarius, and Streptococcus sanguis, Salmonella, Campylobacter, including Campylobacter sputum, Antinomyces, including Actinomyces naeslundii and Actinomyces viscosus, Escherichia coli, Clostridium difficile, Staphylococcus, including S. aureus, Shigella, Pseudomonas, including P. aeruginosa, Eikenella corrodens, Actinobacillus actinomycetemcomitans, Bacteroides gingivalis, Capnocytophaga, including Capnocytophaga gingivalis, Wolinell recta, Bacteriodes intermedius, Mycoplasma, including Mycoplasma salivarium, Treponema, including Treponema denticola, Peptostreptococcus micros, Bacteriodes forsythus, Fusobacteria, including Fusobacterium nucleatum, Selenomonas sputigena, Bacteriodes fragilis, Enterobacter cloacae and Pneumocystis. Also included are protozoal infections, such as infection by Cryptosporidium parvum and Giardia lamblia; ameobic infections, such as infection by Entameoba histolytica or Acanthameoba; fungal infections, such as infections by Candida albicans and Aspergillus fumigatus, and parasitic infections, such as infections by A. castellani and Trichinella spiralis. The method is useful for treating infections of various organs of the body, but is particularly useful for infections of the skin and gastrointestinal tract.
Polymers which are particularly suitable for the present method include polymers which can possess key characteristics of naturally occurring cytotoxic peptides, in particular, the ability to form amphipathic structures. The term xe2x80x9camphipathicxe2x80x9d, as used herein, describes a three-dimensional structure having discrete hydrophobic and hydrophilic regions. Thus, one portion of the structure interacts favorably with aqueous and other polar media, while another portion of the structure interacts favorably with non-polar media. An amphipathic polymer results from the presence of both hydrophilic and hydrophobic structural elements along the polymer backbone.
In one embodiment, the polymer to be administered polymer comprises a monomer of Formula I, 
wherein X is a covalent bond, a carbonyl group or a CH2 group, Y is an oxygen atom, an NH group or a CH2 group, Z is an spacer group, R is a hydrogen atom or a methyl or ethyl group, R1, R2 and R3 are each, independently, a hydrogen atom, a normal or branched, substituted or unsubstituted C1-C18-alkyl group, an aryl group or an arylalkyl group. Suitable alkyl substituents include halogen atoms, such as fluorine or chlorine atoms.
In the case in which at least one of R1-R3 is a hydrogen atom, the monomer can also exist in the free base, or amino form, that is, as the neutral conjugate base of the ammonium cation. The polymer comprising such a monomer can be administered in the protonated, cationic form, such as a salt of a pharmaceutically acceptable acid, or in the free base form. Suitable acids include hydrochloric acid, hydrobromic acid, citric acid, lactic acid, tartaric acid, phosphoric acid, methanesulfonic acid, acetic acid, formic acid, maleic acid, fumaric acid, malic acid, succinic acid, malonic acid, sulfuric acid, L-glutamic acid, L-aspartic acid, pyruvic acid, mucic acid, benzoic acid, glucoronic acid, oxalic acid, ascorbic acid, and acetylglycine. In either case, at physiological pH following administration, a plurality of amino groups will be protonated to become ammonium groups, and the polymer will carry an overall positive charge.
The spacer group is a component of the polymer side chain and connects the amino or ammonium group to the polymer backbone. The amino or ammonium group is, thus, a pendant group. The spacer group can be a normal or branched, saturated or unsaturated, substituted or unsubstituted alkylene group, such as a polymethylene group xe2x80x94(CH2)nxe2x80x94, wherein n is an integer from about 2 to about 15. Suitable examples include the propylene, hexylene and octylene groups. The alkylene group can also, optionally, be interrupted at one or more points by a heteroatom, such as an oxygen, nitrogen (e.g, NH) or sulfur atom. Examples include the oxaalkylene groups xe2x80x94(CH2)2O[(CH2)2O]n(CH2)2xe2x80x94, wherein n is an integer ranging from 0 to about 3.
Examples of monomers of Formula I having quaternary ammonium groups include 2-trimethylammonium-ethylmethacrylate, 2-trimethylammoniumethylacrylate, N-(3-trimethylammoniumpropyl)methacrylamide, N-(6-trimethylammoniumhexyl)acrylamide, N-(3-trimethylammoniumpropyl)acrylamide, and N-(4-trimethylammoniumbutyl)allylamine, each of which also includes a counter anion. Examples monomers of Formula I having an amino group include allylamine and N-(3-dimethylaminopropyl)acrylamide.
Polymers to be administered which have quaternary ammonium groups or protonated amino groups will further comprise a pharmaceutically acceptable counter anion, such as anions which are conjugate bases of the pharmaceutically acceptable acids discussed above, for example, chloride, bromide, acetate, formate, citrate, ascorbate, sulfate or phosphate. The number of counter anions associated with the polymer prior to administration is the number necessary to balance the electrical charge on the polymer.
The polymer can also be a copolymer further comprising a hydrophobic monomer. The hydrophobic monomer can comprise a side chain bearing a hydrophobic group, such as a straight chain or branched, substituted or unsubstituted C3-C18-alkyl group or a substituted or unsubstituted aryl group. Examples of suitable hydrophobic monomers include styrene, N-isopropylacrylamide, N-t-butylacrylamide, N-n-butylacrylamide, heptafluorobutylacrylate, N-n-decylallylamine, N-n-decylacrylamide, pentafluorostyrene, n-butylacrylate, t-butylacrylate, n-decylacrylate, N-t-butylmethacrylamide, n-decylmethacrylate, and n-butylmethacrylate.
Examples of copolymers comprising a monomer of Formula I and a hydrophobic monomer include poly(N-(3-dimethylaminopropyl)acrylamide-co-N-(n-butyl)acrylamide) or salts thereof with pharmaceutically acceptable acids. Other examples of suitable copolymers include poly(2-trimethylammoniumethylmethacrylate-co-styrene) chloride, poly(2-trimethylammoniumethylmethacrylate-co-N-isopropylacrylamide) chloride, poly(2-trimethyl-ammoniumethylmethacrylate-co-heptafluorobutylacryl) chloride, poly(3-trimethylammoniumpropylmethacrylate-co-styrene) chloride, poly(3-trimethylammonium-propylmethacrylate-co-N-t-butylacrylamide) chloride, poly(3-trimethylammoniumpropylmethacrylate-co-N-n-butylacrylamide) chloride, and poly(N-(3-trimethylammoniumpropyl)allylamine-co-N-n-decylallylamine). Each of these ionic copolymers can also be employed with counter ions other than chloride, for example, a conjugate base of a pharmaceutically acceptable acid.
In a further embodiment, the polymer to be administered comprises a monomer of Formula I, a hydrophobic monomer and a neutral hydrophilic monomer, such as acrylamide, methacrylamide, N-(2-hydroxyethyl)acrylamide or 2-hydroxyethylmethacrylate. Examples of polymers of this type include terpolymers of N-(3-trimethylammonium-propyl)methacrylamide/N-isopropylacrylamide/2-hydroxyethyl-methacrylate, N-(3-trimethylammonium-propyl)methacrylamide/N-n-decylacrylamide/2-hydroxyethylmethacrylate, N-(3-trimethylammoniumpropyl)methacrylamide/N-t-butylmethacrylamide/methacrylamide, N-(3-trimethylammonium-propyl)methacrylamide/n-decylacrylate/methacrylamide, 2-trimethylammoniumethylmethacrylate/n-butyl-acrylate/acrylamide, 2-trimethylammonium-ethylmethacrylate/t-butylacrylate/acrylamide, 2-trimethylammoniumethylmethacrylate/n-decyl-acrylate/acrylamide, 2-trimethylammonium-ethylmethacrylate/n-decylmethacrylate/methacrylamide, 2-trimethylammoniumethylmethacrylate/N-t-butyl-methacrylamide/methacrylamide and 2-trimethylammoniumethylmethacrylate/N-n-butyl-methacrylamide/methacrylamide.
The polymer to be administered can be an addition polymer having a polymer backbone such as a polyacrylate, polyacrylamide poly(allylalcohol), poly(vinylalcohol), poly(vinylamine), poly(allylamine), or polyalkyleneimine backbone. The polymer can have a uniform backbone if it is composed of monomers derived from a common polymerizable unit, such as acrylamide. If the polymer is a copolymer, it can also comprise a mixed backbone, for example, the monomer of Formula I can be an acrylamide derivative, while the hydrophobic monomer can be a styrene derivative. The polymers disclosed herein include examples of both uniform and mixed backbones.
The polymers of use in the present method also include condensation polymers, wherein polymerization of monomers is accompanied by the release of a small molecule, such as a water molecule. Such polymers include, for example, polyesters and polyurethanes.
The polymers of use in the present method are preferably substantially nonbiodegradable and nonabsorbale. That is, the polymers do not substantially break down under physiological conditions into fragments which are absorbable by body tissues. The polymers preferably have a nonhydrolyzable backbone, which is substantially inert under conditions encountered in the target reion of the body, such as the gastrointestinal tract.
The composition of the copolymers to be administered can vary substantially. The copolymer can comprise from about 95 mole percent to about 5 mole percent, preferably from about 20 mole percent to about 80 mole percent, of a monomer of Formula I. The copolymer can also comprise from about 95 mole percent to about 5 mole percent, preferably from about 20 mole percent to about 80 mole percent, of a hydrophobic monomer.
Other examples of polymers which are of use in the present method are disclosed in U.S. patent application Ser. Nos. 08/482,969, 08/258,477, 08/258,431, 08/469,659 and 08/471,769, the contents of each of which are incorporated herein by reference.
The polymer to be administered will, preferably, be of a molecular weight which is suitable for the intended mode of administration and allows the polymer to reach and remain within the targeted region of the body for a period of time sufficient to interact with the infecting organism. For example, a method for treating an intestinal infection should utilize a polymer of sufficiently high molecular weight to resist absorption, partially or completely, from the gastrointestinal tract into other parts of the body. The polymers can have molecular weights ranging from about 500 Daltons to about 500,000 Daltons, preferably from about 2,000 Daltons to about 150,000 Daltons.
The polymers which are useful in the present method can be prepared by known methods. A first method includes the direct polymerization of a monomer, such as trimethylammoniumethylacrylate chloride, or a set of two or more monomers, such as trimethylammoniumethyl-acrylate chloride, N-n-butylacrylamide and acrylamide. This can be accomplished via standard methods of free radical, cationic or anionic polymerization which are well known in the art. Due to reactivity differences between two monomers, the composition of a copolymer produced in this way can differ from the composition of the starting mixture. This reactivity difference can also result in a non-random distribution of monomers along the polymer chain.
A second method proceeds via the intermediacy of an activated polymer comprising labile side chains which are readily substituted by a desired side chain. An example of a suitable activated polymer is the succinimide ester of polyacrylic acid, poly(N-acryloyloxysuccinimide) (also referred to hereinafter as xe2x80x9cpNASxe2x80x9d), which reacts with nucleophiles such as a primary amine to form a N-substituted polyacrylamide. Another suitable activated polymer is poly(para-nitrophenylacrylate), which react with amine nucleophiles in a similar fashion.
Polymers suitable for use in the present method can also be prepared by addition of a side chain to a preformed polymer. For example, poly(allylamine) can be alkylated at the amino nitrogen by one or more alkylating agents. For example, one fraction of amino groups can be alkylated using a normal or branched C3-C18-alkyl halide, such as n-decyl bromide, while another fraction can be alkylate by a quaternary ammonium-containing alkyl halide, such as 1-trimethylammonium-4-bromombutane.
A copolymer having a polyacrylamide backbone comprising amide nitrogens bearing two different substituents can be prepared by treating p(NAS) with less than one equivalent (relative to N-acryloyloxysuccinimide monomer) of a first primary amine, producing a poly(N-substituted acrylamide-co-N-acryoyloxysuccinimide) copolymer. Remaining N-acryoyloxysuccinimide monomer can then be reacted with, for example, an excess of a second primary amine to produce a polyacrylamide copolymer having two different N-substituents. A variety of copolymer compositions can, thus, be obtained by treating the activated polymer with different proportions of two or more amines.
An additional aspect of the present invention is a method for treating a microbial infection in a mammal, such as a human, comprising administering to the mammal a therapeutically effective amount of a polymer having an amino group or an ammonium group within the polymer backbone. The polymer can have, for example, a polymethylene backbone which is interrupted by one or more amino or ammonium groups. An example of a polymer of this type is poly(decamethylenedimethylammonium-co-ethylenedimethylammonium) bromide, which is synthesized via the reaction of N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine and 1,10-dibromodecane. The polymer can also be administered in association with anions other than bromide, such as chloride or acetate anions. Other examples include poly(alkyleneimines), for example, poly(ethyleneimine). Such polymers can comprise secondary or tertiary amino groups, salts of such groups with pharmaceutically acceptable acids, and/or quaternary ammonium groups.
As discussed below in Example 35, several polymers described herein were tested for in vitro activity against Cryptosporidium parvum infectivity in mammalian cell culture. Of these, poly(TMAEMC-co-styrene), described in Example 7, was most active, exhibiting greater than 90% inhibition of C. parvum infectivity relative to the control when applied as a 0.1 mg/mL solution in dimethylsulfoxide. The remaining polymers tested also showed significant anti-Cryptosporidium activity.
The invention will now be further and specifically described by the following examples.